Tool for drilling cooling passages in turbine blades

ABSTRACT

A tool for electrolytically drilling a lateral branch from a passage in a metal workpiece which comprises a tube of insulating material having holes in its side wall and a wire within the tube which is substantially thinner than the bore of the tube. The wire is off-set relative to the center of the tube and is positioned opposite to the holes in the side wall of the tube.

United States Patent 1 3,910,832 Tuck et al. Oct. 7, 1975 [54] TOOL FOR DRILLING COOLING PASSAGES IN TURBINE BLADES [56] References Cited [75} Inventors: Ernest Victor Tuck; Derek Aubrey IT D TATES ATENTS Glew; Ian Dennis p all of 3,290,237 l2/l966 Abt et al 4, 204/284 x FiitOl'l, England 3,445,372 5/!969 Fromson 204/284 X [73] Assignee: Secretary of State for Defence in Her FOREIGN PATENTS OR APPLICATIONS Britannic Majestys Governmem 934,557 8/!963 United Kingdom 204/224 M the United Kingdom of Great Britain and Noflhern Ireland London Primary Examiner-1ohn H. Mack England Assistant ExaminerD. R, Valentine [22] Ffl d; M 16, 1973 Attorney, Agent, or Firm-Stevens, Davis, Miller &

Mosher [2!] Appl. No.: 360,980

Related U.S. Application Data [57] ABSTRACT Division of 1971- A tool for electrolytically drilling a lateral branch abandoned from a passage in a metal workpiece which comprises i a tube of insulating material having holes in its side [30] Fore'gn Appl'cat'on pr'omy Dina wall and a wire within the tube which is substantially Aug, 27, 1970 United Kingdom 41357/70 thinner than the bore of the tube. The wire is off-set relative to the center of the tube and is positioned op- [52] US. Cl. 204/284 posite to the holes in the side wall of the tube. [Sl] Int. Cl B0lk 3/04 581 Field of Search 204/224 M. 284 7 Drawmg F'gms Y & ,/2 l4 i F i [22 2 Q 7 az Sheet 1 of 4 I nventor A ttorney US. Patent 0a. 7,1975 Sheet 2 of4 3,910,832

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L w, m i Q m\\\ *2 Q 7 Inventor V///M/ //W//// M Attorney US. Patent Oct. 7,1975 Sheet 4 of4 3,910,832

In ven (or A ltarnn u TOOL FOR DRILLING COOLING PASSAGES IN TURBINE BLADES This is a division of application Ser. No. l74,037, filed Aug. 23, I971 now abandoned.

In a gas turbine, one way of cooling the leading edg of a turbine blade is to provide a longitudinal passage close to the leading edge, a second'longitudinal passage to the rear of the first, and a series of nozzles connect ing the second passage to the first, the nozzles being spaced along the length of the blade. In use, cooling fluid is supplied to the root end of the second passage, and passes as jets into the first passage, so as to exert a cooling effect on the side of the first passage closest to the leading edge. 1

Hitherto there has been great difiiculty in making a series of nozzles connecting two passages in this manner.

The present invention concerns methods and tools which have been devised primarily for making such nozzles in gas turbine blades. The examples described in detail below therefore relate to gas turbine blades. However, methods and tools embodying the invention are applicable also to other purposes, for example in the making of instruments.

According to this invention a method of electrolytically drilling a lateral branch from a passage in a metal workpiece comprises the steps of:

inserting into the passage a tube which is of insulating material, makes a clearance fit in the passage, contains an electrode, and has in its side wall a hole;

supplying electrolyte to the bore of the tube;

maintaining pressure upon the electrolyte in the bore of the tube whereby a jet of electrolyte emerges from the hole and impinges on the workpiece;

and applying and maintaining a voltage between the electrode and the workpiece.

In particular, a method of electrolytically drilling a plurality of lateral branches from a passage in a metal workpiece comprises the steps defined above, modified by the use of a tube which has a like plurality of holes in its side wall.

Preferably the tube is a tube of fused quartz containing a wire which makes a clearance fit in the tube and constitutes the electrode, the tube having the hole or plurality of holes in its side wall.

The accompanying drawings serve to illustrate the invention and show further details which are advantageous for some purposes but not essential. In these drawings:-

FIG. 1 is a diagrammatic side elevation of an apparatus for making a series of nozzles connecting a second passage to a first passage in a gas turbine blade;

FIG. 2 is a vertical section, on a much larger scale, of a fragment ofa gas turbine blade and the lower part of a tool; and

FIG. 3 is a cross section on the line Ill-III in FIG. 2.

As shown in FIG. I, a gas turbine blade 6 is mounted in a jig 20 on a work table 22. The table is mounted on the frame 24 of the apparatus, via a slide 26. The slide 26 can be displaced horizontally in two directions at right angles, by controls indicated diagrammatically at 28 and 30, and the table 22 can be raised and lowered relatively to the slide by means ofa control 32, and can be rotated about a vertical axis AA by a control 34.

The blade is prepared with a first passage 2 and a second passage 4, and the jig 20 is constructed so as to ensure that the axis of the passage 4 is vertical.

A tool in the form of a tube 8 is carried vertically by a mounting 36, fixed to the upper part of the frame of the apparatus. A pump 38 and a pipe 40 serve to supply a flow of electrolyte to the interior of the tube.

A source of direct current 42 has its positive pole connected at 44 to the table 22, and has its negative pole connected at 46 to an insulated terminal on the mounting 36, there being an internal connection, not shown, from this terminal to an electrode within the tube 8.

In use, the controls 28 and 30 are used to bring the second passage 4 beneath the tool 8, and the control 34 is used to rotate the turbine blade 6 until a plane containing the axes of the passages 2 and 4 is aligned with the holes (described below) in the tool 8. Then the turbine blade is raised by means of the control 32 so that the tool 8 enters the passage 4, and assumes the position shown in FIGS. 2 and 3.

As shown in FIGS. 2 and 3, the first passage 2 and second passage 4 are cylindrical, and lie with the first passage near the leading edge 5 of the turbine blade 6, and the second passage, which is larger, behind the first.

The tool is a circular-sectioned tube 8 of fused quartz, closed at its lower end by a plug 10. Within the tube is an electrode 12 of round metal wire. The electrode is fixed to the tube by resin bonding at each end of the tube.

The series of holes in the tube are shown at 14, and the series of branch nozzles produced in the blade are shown at I6. As illustrated in FIGS. 2 and 3, the electrode wire 12 lies against the internal surface of the tube 8 opposite to the holes.

The dimensions of the example shown in FIGS. 2 and 3 are as follows:-

Diameter of the second passage in the blade 0.06 inch (1.53 mm) External diameter of tool 005 inch (1.27 mm) Diameter of bore of tool 0.02 inch (0.5l mm) Diameter of wire 0.003 inch (0.08 mm) Diameter of outer ends of holes in tube 0.005 inch (0.13 mm) The size and shape of the nozzles formed between the second passage and the first passage in the blade depends somewhat on the voltage applied and on the pressure of electrolyte. The holes tend to have a bellmouth shape, with the widest end towards the second passage, and this is desirable, because it produces a nozzle effect. Preferably, with the dimensions given, the electric supply is about 30 volts, and the holes are 0.020 inch (0.5lmm) diameter where they leave the second passage, and 0.010 inch (0.25 mm) diameter where they break into the first passage, the thickness of the material between the second and first passages being 0.0 l 25 inch (032mm). The spacing between the holes should be not less than 0.020 inch (051mm). The electrolyte in the pipe 40 is at a pressure of about to lbs./sq.inch (700 to 1 I00 kN/m preliminary tests will show the length of time for which the process should continue, in order to ensure that all the nozzles are broken through from the second passage to the first passage.

The holes in the tool may be either cylindrical, or somewhat tapering, with the smallest diameter at the outside of the tube. They may be formed by mechanical drilling, or by electron beam drilling. ln the latter case, each hole is made by first forming a hole completely through both opposite sides of the tube, and then plugging the hole on one side.

Spent electrolyte escapes upwards in the clearance between the tool 8 and the wall of the second passage 4, and can be collected by means not shown.

We claim:

1. A tool for electrolytically drilling a lateral branch from a passage in a metal workpiece, comprising a tube of insulating material having a hole in its side wall; a

wire within the tube lying against an internal surface thereof opposite said hole and fixed at each end to said tube, said wire being substantially thinner than the bore of the tube and off-set relative to the longitudinal axis of the tube; and a plug closing one end of said tube, said hole lying to one side of a plane through said axis and said wire lying wholly on the other side of said plane.

2. A tool according to claim 1, wherein there are additional holes in the side wall of the tube, which together with the said hole form a series, spaced along the tube.

3. A tool according to claim 1, wherein the ratio of wire diameter to bore diameter is about 3 to 20.

4. A tool according to claim 1, wherein the tube of insulating material is made of fused quartz. 

1. A TOOL FOR ELECTROLYTICALLY DRILLING A LATERAL BRANCH FROM A PASSAGE IN A METAL WORKPIECE, COMPRISING A TUBE OF INSULATING METERIAL HAVING A HOLE IN ITS SIDE WALL: A WIRE WITHIN THE TUBE LYING AGAINST AN INTERNAL SURFACE THEREOF OPPOSITE SAID HOLE AND FIXED AT EACH END TO SAID TUBE, SAID WIRE BEING SUBSTANTIALLY THINNER THAN THE BORE OF THE TUBE AND OFF-SET RELATIVE TO THE LONGITUDINAL AXIS OF THE TUBE: AND A PLUG CLOSING ONE END OF SAID TUBE SAID HOLE LYING TO ONE SAID OF A PLANE THROUGH SAID AXIS AND SAID WIRE LYING WHOLLY ON THE OTHER SIDE OF SAID PLANE.
 2. A tool according to claim 1, wherein there are additional holes in the side wall of the tube, which together with the said hole form a series, spaced along the tube.
 3. A tool according to claim 1, wherein the ratio of wire diameter to bore diameter is about 3 to
 20. 4. A tool according to claim 1, wherein the tube of insulating material is made of fused quartz. 